Items not consistently showing in Azure DevOps backlog

In Azure DevOps (Services ) I have customized the scrum process template with three custom work order types to mimic Epics, Features and User Stories.

I have only one Area, and one Team. We want to be able to utilize Boards, but we don't really operate in "Sprints".

I have around 3k total work items on User Story level, 470 of which are assigned to me. Only the Epic Level Items are showing for me in Boards.

When I look in the Backlog on the User Story level, I'm getting this message: "Filtering 1000 out of 3402 items. Filter the next 1000 items"

This makes sense, but DevOps isn't consistently showing the items when I click the "Filter next 1000 items link", and I would expect that if I filter the items by Assigned to = @me I would immediately see the 470 items assigned to me.

It seems like the initial filter is causing items to not show in Boards as well as Backlog possibly based on the backlog order.

If I flip the switch to show Parents everything is visible.

Also, sometimes DevOps is changing the number of total Backlog Items it's mentioning in the filter message : Filtering 3408 out of 5779 items. Filter the next 1000 items

Is there a way for me to dial in on the filter settings, or can someone see where I might have gone wrong in my setup?

I can reproduce the same with you:

It's correct behavior. This is because Parent will show or hide hierarchy of work items. If you toggle on parent after you enable the filter with Assigned to=@me,it will include the related(child/parent) work items and change the filtering work item result.

In addition, there is another option Keep hierarchy with filters, if you toggle it on and then toggle on/off parent, the filter result will be different.

Please refer to the doc here for the details:

Please note the Parent Work Item isn't a filter function for Backlogs, it enables you to focus on one or more select work items(features or epics) on the page.

I would expect that if I filter the items by Assigned to = @me I would immediately see the 470 items assigned to me.

It works on my side, you can refresh the page, and check again.

Is there a way for me to dial in on the filter settings, or can someone see where I might have gone wrong in my setup?

There is no way to dial in the filter setting, but you can click Create Query option, on the query, add one more filter to check assgined to= @me items for confirmation, and you can also change the filter in the query.